RE: ElectroMagnetic Compatibility and Tesla coils (fwd)
---------- Forwarded message ----------
Date: Fri, 24 Apr 1998 12:05:22 -0700
From: Michael Baumann <baumann-at-proton.llumc.edu>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: RE: ElectroMagnetic Compatibility and Tesla coils (fwd)
Purely observed, but for your information:
My 360VA 3.5" coil will cause the following during operation:
My modem will disconnect [phone lines run directly over the area where I
fire my coil]
my 900Mhz phone becomes unusable during the run.
on one occasion, I had my alarm system (900Mhz wireless) get confused. Just
took a press of the "self-test" button to clear it.
This coil runs at about 490Khz
My 6.25" coil at 720VA on the otherhand:
introduces mild interference on my 900Mhz line.
Causes extreme complaints about the noise from my wire (3' long arcs are so
much louder :) ]
and that's about it.
This coil runs somewhere around 220Khz (guestimated)
Both light up my "Bud light" [4' flourescent] about 6 ft away (granted the
does a much better job)
My Garage door opener still works fine, despite a couple of direct strikes
My Pager and PalmPilot have survived on my hip (I forget I was wearing them)
even when I was getting zapped by my Variac due to the charge on my body.
Mind you, I don't go out of my way to do this.. but I've been very lucky so
Michael Baumann Optivus Technology Inc.|Loma Linda University Medical
San Bernardino, California. (909)799-8308 |Internet: baumann-at-llumc.edu
> -----Original Message-----
> From: Tesla List [mailto:tesla-at-pupman-dot-com]
> Sent: Friday, April 24, 1998 10:35 AM
> To: tesla-at-pupman-dot-com
> Subject: ElectroMagnetic Compatibility and Tesla coils (fwd)
> ---------- Forwarded message ----------
> Date: Fri, 24 Apr 1998 08:13:07 -0700
> From: Jim Lux <jimlux-at-earthlink-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: ElectroMagnetic Compatibility and Tesla coils
> I have just been engaged in an effort to design some equipment
> for EMC, and
> it occurred to me that there has been a lot of discussion on the
> list about
> TC's and their unfortunate effect on various electronic equipment: radios,
> clocks, PC's, etc. Some of this seems a bit apocryphal to me, although
> there are significant effects.
> Here is my concern: Virtually all modern electronic equipment
> PC's) has to meet fairly stringent EMC requirements, both to keep
> interference inside, but also to insure that it's behavior isn't corrupted
> by outside signals (e.g. a TC output). At the simplest level this is
> accomplished by putting it in a metal box, although in practice, this
> doesn't even get close to meeting the fairly stringent CE and FCC
> I can see an electronic device being affected, operationally, by the RF
> from TC, but as for actual damage, I find it more unlikely. Modern
> Electrostatic Discharge (ESD) precautions on equipment make it pretty
> immune to fairly high voltage (although low energy) zaps.
> Of course, the cost of the item and whether it is perceived as "mission
> critical" do have an effect on how much time the designer spend on EMC.
> $2000 PC's would be better than a $10 clock radio for instance.
> Has anyone made any *Calibrated* measurements of the EM fields at some
> distance from a typical small/medium sized coil (less than 2 kVA)?
> We all know that Greg's 130 kVA monster will destroy equipment, just from
> ohmic heating on a direct strike. A simple ballpark far field calculation
> (which is certainly not valid, given the long wavelength of the
> typical TC)
> would show that a 500 VA (e.g. a NST) coil would produce an average RF
> power density of around 10 Watts per square meter at a distance of 2
> meters. This assumes a point source, isotropic radiator, which a
> TC that is
> some very small fraction of a wavelength would be. The peak RF power
> would, of course, be higher, due to the pulsed nature of a TC.
> Those of you that have actually destroyed equipment (first hand,
> not friend
> of a friend of a friend who heard it from a post on the Tesla list), how
> far away was it? what power TC were you running? was the cover off the
> equipment? (I know you all never take the cover off your PC,
> right???) what
> sorts of cables were hooked up, to where?
> For reference, my little 100 watt coil (which does NOT have any line
> filters) doesn't seem to have any effect on a properly assembled
> PC that is
> sitting on the same bench, about 2 feet away. The "digital pbx" phones, on
> the other hand, are screwed up at a distance of 20-30 feet, no
> doubt due to
> the lousy installation of the phone lines which act as a huge antenna to
> absorb the significant radiated RF power (a fluorescent tube lights up 10
> feet away). ALthough, the phones are disrupted during operation, they are
> not damaged.
> Comments solicited...I'm going to do some better calculations on
> the fields
> and the interference levels relative to FCC and CE specs for EMC.